Mechanical fuse, a neck cord comprising a mechanical fuse and a method of connecting a mechanical fuse to a neck cord

ABSTRACT

The invention defines a mechanical fuse ( 20 ) for a neck cord ( 30 ). The mechanical fuse opens the neck cord when a pulling force component in a predetermined direction ( 70 ) exceeds a predetermined fuse force at which a rupture element ( 50 ) included in the mechanical fuse is designed to break. The rupture element has a break plane ( 51 ) at which breakage will occur when the pulling force component causes the stress in the break plane to exceed the value determined by said fuse force. The mechanical fuse further comprises a housing ( 60, 61, 62 ) that is arranged to guide the component of the pulling force in said predetermined direction ( 70 ) to the break plane whereas the transfer of a force component having another direction is suppressed.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a mechanical fuse and a neck cord comprisingsaid mechanical fuse. Such a mechanical fuse breaks at a predeterminedfuse force to prevent injuries and accidental loss. The inventionfurther relates to a method of connecting said mechanical fuse to theneck cord.

BACKGROUND OF THE INVENTION

Mechanical fuses are known in the art. U.S. Pat. No. 5,533,238 disclosesa breakaway cord connector made from two identical cord connectorbodies. Each body has a cord end clamp and a mating end. The mating endfits into the identical mating end of the opposite unit and whenconnected the mating ends breakaway at a preset tension.

A disadvantage of the known mechanical fuses is that the value of thepulling force needed to cause a breaking may be dependent on the actualapplication and use making them less suitable for a neck cord carrying apersonal help button.

It is an object of the invention to provide a mechanical fuse for a neckcord in which the actual application and use have a reduced influence onthe break force needed to break the fuse.

SUMMARY OF THE INVENTION

The object is achieved with a mechanical fuse according to claim 1. Saidmechanical fuse comprises a rupture element and housing coupled to therupture element. The neck cord is coupled to the mechanical fuse at thefirst and second coupling means. The pulling force acting on the firstand second coupling means is a vector and its orientation and value maydiffer dependent on the actual application and use. The housing engageswith the rupture element at either side of the break plane to prevent apossible bending of the rupture element. At the same time the ruptureelement is moveable with respect to the housing in the predetermineddirection such that a force component in the predetermined direction istransferred to the break plane. When in use the neck cord is pulled witha pulling force a component of said pulling force having a directioncorresponding to the predetermined direction will be transferred by thehousing to the break plane of the rupture element. When said forcecomponent exceeds a predetermined fuse force the rupture element willbreak in portions. At least one portion will slide away from the housingresulting in an opening of the neck cord. The housing suppresses thetransfer to the break plane of a force component of the pulling forcehaving another direction than said predetermined direction and preventsthat the rupture element is bended relative to the predetermineddirection. Thus in an application with force components acting on themechanical fuse in another direction than said predetermined directionsaid force components have a reduced contribution to the stress on therupture element thereby preventing that those force components cause abreaking at a value other than the predetermined fuse force.

In an embodiment of the mechanical fuse after breakage the ruptureelement breaks in a first portion and a second portion and the pullingforce causes the first and second portions to slide away from thehousing in opposite direction thereby opening the neck cord.

In a further embodiment after breakage the first portion of the ruptureelement is moveable with respect to the housing while the second portionretains the housing to prevent that the housing is lost as a separatepart. In a further embodiment the housing and the rupture element haveelongated mating shapes. In a further embodiment the housing and ruptureelement have mating cylindrical shapes. In a further embodiment thecylindrical shaped housing and rupture element have an elliptical crosssection. A mechanical fuse according to this embodiment may have a slimand elongated shape which makes the mechanical fuse less notable.Further do the mating shapes with elliptical cross section prevent thata rotation of the first coupling means relative to the second couplingmeans causes a torque on the break plane.

In a further embodiment of the mechanical fuse the rupture element hasthe shape of an hourglass or dumbbell. Under influence of a pullingforce having a force component in the predetermined direction therupture element will break at the break plane where its cross sectionhas the smallest area, provided said force component is larger than thepredetermined fuse force. The housing may for example be arranged as abushing around the hourglass shaped rupture element preventing a bendingand/or torque of the rupture element such that a transfer of forcecomponents of a pulling force acting on the mechanical fuse in adirection not parallel to the longitudinal axis are suppressed. Thehousing may be made of a stiff material to prevent in an assembledmechanical fuse a possible bending of the rupture element. Or thehousing may have a shape that is difficult to distort.

In a further embodiment the elongated shaped rupture element ispositioned perpendicular to the direction of the line crossing the firstand second connection means to which the neck cord cable ends areconnectable. In this embodiment the force component acts on the breakplane of the rupture element as a shear force and the housing isarranged to suppress a transfer of force components of the pulling forceacting on the mechanical fuse in a direction not parallel to thepredetermined direction. The housing may comprise two mating portionswhich when attached to each other are secured by the rupture element. Inthis embodiment each of the mating portions may be connectable to acorresponding end of the neck cord.

The value of the predetermined fuse force needed to break the fuse andopen the neck cord is determined by the material and value of a crosssection of the rupture element. This provides the advantage that therupture element can be designed to make the mechanical fuse suitable fora specific application. A further advantage is that by controlling inthe manufacturing process the material quality as well as the crosssection dimensions of the rupture element the tolerance in the value ofpredetermined fuse force can be kept within limits that are determinedby and required for the application of the mechanical fuse.

For example in an application where a neck cord is used to carry apersonal help button these tolerance limits of the predetermined fuseforce are chosen such that on the one hand there is a small chance oflosing the personal help button due to an accidental stress causing abreak of the rupture element due to a low fuse force and on the otherhand there is a minimal risk of serious injury caused by a non breakagedue to a high fuse force. Hence the rupture element must be designedsuch that the tolerance in its predetermined fuse force guarantees thatthe predetermined fuse force is between these low and high fuse forces.After extensive testing it has been determined that for this particularapplication the predetermined fuse force is chosen to be in the range of40 to 50 N. Hence a neck cord carrying a personal help button andcomprising the mechanical fuse according to the invention providesimproved security and safety to its user.

In a further embodiment the rupture element is made of Polyoxymethyleneor POM. This material has a tensile strength that with a desired fuseforce in the range of 40 to 50 N results in a value of the cross sectionarea of the rupture element in the break plane allowing a compact designof the mechanical fuse. Next to this the POM is chemically resistant andhas sufficient rupture characteristics (relative brittle). Alsopolybutylene terephthalate or PBT could be used.

In a further embodiment the invention defines a method of connecting themechanical fuse according to the above discussed embodiments to a neckcord. For example in an embodiment of the method the housing is put onthe neck cord similar to how a bead is threaded. Next the open ends ofthe neck cord are connected to the coupling means which are included inthe first and second portions of the rupture element. Finally thehousing is pushed over the rupture element to couple it to the ruptureelement. The housing may for example have a snap fit coupling with thesecond portion of the rupture element to keep it on its position. Or asan alternative the method may comprise a next step in which the secondportion is be welded or glued to the housing. After having connected therupture element to the neck cord and having assembled the mechanicalfuse it can be safely used for example for carrying a personal helpbutton.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described, by way ofexample only, with reference to the following drawings, in which:

FIG. 1 shows a neck cord carrying a personal help button;

FIG. 2 shows a graph indicating the risk to not being able to give analarm due to accidental loss and the risk of injury as a function ofbreak force;

FIG. 3 shows forces acting on an embodiment of a rupture element;

FIG. 4 shows forces acting on an embodiment of a mechanical fusecomprising the rupture element of FIG. 3;

FIG. 5 shows a further embodiment of the mechanical fuse of FIG. 4;

FIG. 6 shows an example of parts making up a further embodiment of amechanical fuse;

FIG. 7 shows the assembled mechanical fuse of FIG. 6;

FIG. 8 shows an embodiment of an hourglass shaped rupture element;

FIG. 9 shows an embodiment of a mechanical fuse comprising the ruptureelement of FIG. 8;

FIG. 10 shows an embodiment of a mechanical fuse comprising an elongatedshaped rupture element;

FIG. 11 shows a housing portion of the mechanical fuse of FIG. 10.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a neck cord 30 comprising length adjustment means 35 and amechanical fuse 20 according to the invention. A personal help button 10is attached to the neck cord. The user of the neck cord can request forassistance by pushing the button. The mechanical fuse is included in theneck cord to reduce the risk of entanglement because it breaks when apulling force of the cord on the fuse exceeds the predetermined fuseforce. The mechanical fuse should also be reliable to prevent anaccidental loss of the personal help button by breaking at a smallpulling force of the neck cord acting on the mechanical fuse and causingan unnoticed opening of the loop formed by the neck cord.

FIG. 2 illustrates the two requirements of minimized risk of injury andminimized risk of accidently opening of the neck cord. The horizontalaxis 24 shows the pulling force acting on the mechanical fuse in theneck cord of FIG. 1. The first vertical axis 22 shows the risk that noalarm can be given because the personal help button has been lostwithout the user being aware due to an accidental breaking of themechanical fuse. The risk varies between ‘low’ to ‘high’. The secondvertical axis 23 shows the risk of serious injury caused by not breakingof the fuse while the neck cord is being pulled and a pulling force actson the mechanical fuse. The risk of serious injury also varies from‘low’ to ‘high’. Line 25 in combination with the first vertical axis 22indicate that when the mechanical fuse is breaking at a low pullingforce the risk that no alarm can be given is high because it is likelythat the personal help button will be lost without notice when the neckcord has accidently opened. But when the mechanical fuse is designed tobreak at a higher pulling force this risk will decrease. Line 26 incombination with the second vertical axis 23 indicate that when themechanical fuse breaks at a high pulling force the risk of seriousinjury is high. This risk can be reduced by having the mechanical fusebreaking at a lower pulling force. The intersection of lines 25 and 26provides an optimum 24 which is characterized by having an equal lowrisk on accidental loss and serious injury. After extensive testing ithas been determined that for the application of a personal help buttonattached to a neck cord carried by elderly people the optimum is foundat a predetermined fuse force for the mechanical fuse of 45 N. Whentaking production spread into account the upper and lower limit of thepredetermined fuse force should be 40 N and 50 N. Hence thepredetermined fuse force of the rupture element at which the mechanicalfuse must break should be in the range of 40 N-50 N.

FIG. 3 shows an embodiment of a rupture element 50. The rupture element50 is included in the mechanical fuse 20 and will break when ahorizontal component of the force F acting on it exceeds thepredetermined fuse force at which the rupture element is designed tobreak. The rupture element is designed to have a break plane 51 at whichit is intended to break resulting the rupture element to fall apart infirst and second portions 50, 53, the first portion comprising a firstcoupling means 40 and the second portion comprising the second couplingmeans 45. With horizontal is meant a component of the force F in thedirection of the longitudinal axis 70, see FIG. 4. The rupture element50 shown in FIG. 3 has a first and second coupling means 40, 45 at whichthe cable ends of the neck cord 30 can be attached. A force F acting onthe rupture element 50 has a value and a direction as indicated by thearrows. Said force F results from a pulling force acting on themechanical fuse.

FIG. 4 shows an embodiment of the mechanical fuse 20 according to theinvention. It comprises the rupture element 50 discussed under FIG. 3and a housing 60 fitting around said rupture element. The housing 60engages with the rupture element 50 at either side of the break plane toprevent the pulling force from bending the rupture element with respectto the predetermined direction 70. The housing may be made of a stiffmaterial, or the housing may have a shape that is resistant to bending,such as for example a cylindrical shape. Further is the housing moveablewith respect to the rupture element in a predetermined direction 70,which is a direction of a line crossing the first and second couplingmeans. In the embodiment shown in FIGS. 3- 5, 8 and 9 the ruptureelement 60 has an elongated shape with a longitudinal axis correspondingto a line 70 crossing both the first and second coupling points. Therupture element is designed to break at the break plane 51 and at apredetermined fuse force as a result of the force component F_(x) actingon it. Said force component F_(x) has a direction corresponding to thedirection of the line 70 and results from a pulling force F acting onthe mechanical fuse. A force component F_(y) acting on the ruptureelement having a direction perpendicular to the direction of the line 70does not result in a force acting on the break plane as F_(y) is blockedby the housing. The housing 60 prevents a bending of the rupture elementat its middle portion 52. Hence the housing allows a transfer of apulling force F acting on the first and second coupling point to therupture element to result in the force component Fx acting on the breakplane 51 of the rupture element whereas the housing suppresses atransfer to the break plane of the rupture element of the forcecomponent Fy resulting the pulling force F. Without the housing theseforce components Fy may cause the rupture element to break at anothervalue than at the predetermined fuse force as also F_(y) wouldcontribute to a stress across the break plane. In FIG. 4 the housing 60is attached to the rupture element 50 to prevent that force componentsother than the F_(x) force component 80 in the direction of the line 70act on the rupture element. Said F_(x) force component 80 has a valuecorresponding to the projection of the pulling force 85 on the line 70.The housing transfers the force component 80 in the direction of theline 70 to the break plane of the rupture element, and hence at leastone portion 50, 53 of the rupture element is moveable with respect tothe housing in the direction of the line 70. After breakage the pullingforce causes the first and second portions to slide away from thehousing 60 in opposite directions resulting in opening of the neck cord30 of FIG. 1. In a further embodiment the housing 60 is arranged toattach to the second portion. After breakage of the rupture element thepulling force will cause the first portion to slide away from thehousing 60 in the predetermined direction 70 whereas the second portionretains the housing. This has the advantage that the housing will notfall on the ground where it can cause a risk for people walking around.The second portion and the housing 60 may have clamping means to clampthe housing to the second portion. For example the second portion andthe housing may have a shape that provides a snap fit coupling. Or, asanother example the second portion and the housing may have a roughsurface area to provide a frictional coupling. Or, as another exampleafter assembly of the mechanical fuse the second portion may be glued orlaser welded to the housing 60.

The rupture element 50 may for example have a dumbbell shape such as inFIGS. 3 and 4 having end portions 50, 53 with a larger and a middleportion 52 with a smaller cross section area. The predetermined fuseforce F_(fuse) needed to break the rupture element at the break plane isdependent on the maximum stress σ_(max)[N/m²] or tensile strength thatcan be handled by the material chosen for the rupture element and thearea A of the cross section of rupture element in the break plane wherethe breaking will occur. Assuming a cylindrical shaped middle portion 52the relation between the predetermined fuse force, the material of therupture element and the cross section or diameter D is given by:

F _(fuse) =A*σ _(max)=(π/4)*D ²*σ_(max)

Hence by choice of the material and cross section area at the breakplane of the rupture element its predetermined fuse force is obtained.In the embodiment of the mechanical fuse shown in FIG. 3 the housing 60attached to the rupture element conducts the F_(x) force component 80perpendicular to said break plane 51 and blocks a F_(y) force componentparallel to said break plane. In this embodiment of the mechanical fusethe housing 60 enables a horizontal (in the x-direction) movement of atleast one end portion 53 of the rupture element. This moveable couplingof the rupture element and the housing allows a stretching of therupture element as a result of a pulling force acting on the mechanicalfuse. The pulling force causes a necking of the material used for therupture element until the rupture element 50 breaks at the breakingplane in the middle portion 52. The housing 60 prevents the bending ofthe rupture element 50.

FIG. 5 shows at the left side an embodiment of the mechanical fuse 20comprising the housing 60 and the rupture element 50 having a dumbbellshape. The rupture element has coupling means at its ends to allowcoupling to the neck cord 30. In this example the neck cord ends arelooped through an opening in the end portions 40, 45 of the ruptureelement. To ease the explanation in FIGS. 5, 9 and 10 the housing isshown to be transparent. In this embodiment the housing 60 and therupture element 50 have a mating cylindrical shape. Further these matingshapes are arranged to prevent a rotation of the first coupling means 40relative to the second coupling means 45. The mating shapes may compriselocking means such as a bar in one shape fitting in a correspondinggroove of the other shape. In this embodiment of FIG. 5 the housing hasa rotation blocking bar 64 fitting in a corresponding groove 54 in therupture element 50. The housing prevents that in an assembled mechanicalfuse a torque force 86, 87 acting on the coupling means is transferredto the break plane of the rupture element where the cross section issmaller than at the end portions. Hence the housing suppresses atransfer of a rotational force component of the pulling force to thebreak plane 51. In a further embodiment the rupture element and thehousing have a cylindrical shape with an elliptical cross section. Theelliptical cross section prevents a possible rotation of the firstcoupling means relative to the second coupling means.

FIG. 6 shows another embodiment of a mechanical fuse comprising a firstand second housing portion 61, 62. Each housing portion comprises acoupling means 40, 45 to allow the attachment of a neck cord end. FIG. 6further shows the rupture element which is moveable in a matchingopening 63 in the first and second housing portions. This opening 63 isshown more clearly in FIG. 11. FIG. 6 shows the separate parts of themechanical fuse according to this embodiment of the invention. Themechanical fuse is assembled by moving together the first and secondhousing portions such that they are coupled. Next the rupture element ismoved in the opening of the housing portions to result in the mechanicalfuse as is shown in FIG. 7.

The embodiment of FIG. 7 shows a mechanical fuse 20 for a neck cord 30comprising a rupture element 50 arranged to break at a break plane 51when a break force acting on the rupture element exceeds a predeterminedfuse force. The housing included in the fuse comprises first and secondhousing portions 61, 62 having corresponding mating shapes to enable areleasable engaging of the first and second housing portions. When thehousing portions engage they are moveable relative to each other in thepredetermined direction 70, whereas the mating shapes prevent anyrelative movement in a further predetermined direction 55 perpendicularto the predetermined direction. The first housing portion comprises thefirst coupling means 40 and the second housing portion comprises thesecond coupling means 45. Each housing portion has an opening 63 with ashape that corresponds with the shape of the cross section the ruptureelement to make it fit for receipt of the rupture element 60. When themechanical fuse is assembled the housing portions are releasably coupledto each other such that the openings overlap thereby creating a channelin the further predetermined direction 55. Next the rupture element isfitted in this channel thereby securing the first and second housingportions. The inner surface of the channel and/or the surface of therupture element may be rough to create a frictional coupling between thehousing portions and the rupture element. After assembly the break planeof the rupture element is in parallel with the predetermined directionand perpendicular to the further predetermined direction 55. A pullingforce acting on the first and second coupling means and having acomponent in the predetermined direction 70 is transferred to therupture element because the housing portions are moveable in thepredetermined direction with respect to each other. The pulling forcewill therefore act as a shear force on the rupture element. The matingshapes of the housing portions further provide that in an assembledmechanical fuse a transfer of a force component of the pulling force tothe break plane is suppressed when said force component has anotherdirection than said predetermined direction. As shown in FIG. 7, apulling force component F_(x) acting on the first and second couplingmeans is transferred to the rupture element where it works as a shearforce acting on the break plane 51. In FIG. 7 the pulling forcecomponent Fy has a direction perpendicular to Fx which has a directionparallel to the line 70 crossing the first and second coupling means.The pulling force F_(y) acting on the mechanical fuse is not transferredto the break plane 51. The shapes of the first housing portion may forexample comprise a protrusion and a groove corresponding with a matinggroove and mating protrusion in the second housing portion. Theprotrusion 65 of the first housing portion 61 fitting in thecorresponding groove 66 of the second housing portion 62 contributes toa suppression of the transfer of Fy to the break plane having adirection parallel to the line 70. Further when coupled to each otherthe engaging housing portions make it more difficult to bend themechanical fuse relative to the predetermined direction.

FIG. 8 shows an embodiment of coupling means for a rupture element 50that is included in a mechanical fuse according to an embodiment of theinvention. The neck cord has mushroom shaped cable ends which fit in amatching coupling means which is realized as cavities 40, 45 in thefirst and second portions of the rupture element.

FIG. 9 shows an embodiment of the mechanical fuse comprising the ruptureelement of FIG. 8 and a cylindrical shaped housing which fits around therupture element. In this embodiment the component of the pulling forcein the direction of the line 70 crossing the first and second couplingpoints 40, 45 is transferred to the break plane. The fitting of thehousing 60 around the rupture element is therefore such that the matingof the shapes of the first and second portions and the interior of thehousing allows a stretching in the predetermined direction 70 andprevents a bending and/or torsion of the rupture element 50.

FIG. 10 shows a further embodiment of the mechanical fuse 20 that wasearlier discussed using FIG. 7. Again the neck cord 30 has mushroomshaped cable ends but in this embodiment these fit in matching couplingmeans which are realized as cavities 40, 45 in each of the first andsecond housing portions such as shown in FIG. 11. Each housing portionhas a protrusion 65 fitting in a groove 66 of the other housing portionto which it is releasably coupled. When fitted together the protrusionsand grooves prevent a rotation of the housing portions with respect toeach other. The protrusions fitted in the groove also contribute to astiff housing making it more difficult to bend it. In this embodimentthe component of the pulling force in the direction of the line 70crossing the first and second coupling points 40, 45 is transferred bythe housing portions to the break plane 51 of the rupture element 50.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

Other shapes for the rupture element 50 and the housing 60, 61, 62 arepossible depending for example on the actual application of themechanical fuse 20. Also the first and second coupling point 40, 45 maybe positioned with an offset relative to the line 70 as shown in FIG. 4or FIG. 7. Hence a line crossing the first and second coupling point maycross with the predetermined direction of the shown line 70 instead ofbeing parallel with said line. For example in FIG. 7 the cord may becoupled to the first housing portion 61 at a first coupling point 40close to the top corner 61C and at a second coupling point 45 of thesecond housing portion 62C close to the bottom corner 62C such that afurther line 70C crossing the first and second coupling points at thesecorner positions 61C, 62C is crossing the line in the predetermineddirection 70.

Variations to the disclosed embodiments can be understood and effectedby those skilled in the art in practicing the claimed invention, from astudy of the drawings, the disclosure, and the appended claims. In theclaims, the word “comprising” does not exclude other elements or steps,and the indefinite article “a” or “an” does not exclude a plurality. Anyreference signs in the claims should not be construed as limiting thescope.

1. A mechanical fuse (20) for a neck cord (30) comprising a rupture element (50), the rupture element comprising a break plane (51) and first and second coupling means (40, 45) at either side of the break plane, the first and second coupling means being arranged for connecting to the neck cord, the rupture element being arranged to break at the break plane (51) when a pulling force acting on the rupture element in a predetermined direction (70) exceeds a predetermined fuse force; a housing (60) being coupled to the rupture element wherein the housing is arranged to engage with the rupture element at either side of the break plane to prevent the pulling force from bending the rupture element relative to the predetermined direction, the housing being moveable with respect to the rupture element in the predetermined direction.
 2. A mechanical fuse (20) according to claim 1 wherein said predetermined direction (70) is parallel to the direction of a line (70) crossing the first and second coupling means.
 3. A mechanical fuse (20) according to claim 1 wherein the rupture element (50) is arranged to break in a first portion and a second portion such that after breakage the pulling force causing the first and second portions to slide away from the housing (60) in opposite directions thereby opening the neck cord (30).
 4. A mechanical fuse (20) according to claim 1 wherein the rupture element (50) is arranged to break in a first portion and a second portion, and wherein after breakage the first portion is moveable with respect to the housing (60), the housing being arranged to attach to the second portion such that after breakage the pulling force causes the first portion to slide away from the housing (60) in the predetermined direction (70) thereby opening the neck cord (30), the second portion retaining the housing.
 5. A mechanical fuse (20) according to claim 4 wherein the second portion and the housing (60) comprise clamping means arranged for clamping the housing to the second portion.
 6. A mechanical fuse (20) according to claim 5 wherein the second portion and the housing (60) are arranged for a snap fit coupling to each other.
 7. A mechanical fuse (20) according to claim 4 wherein the second portion and the housing (60) are arranged to have a frictional coupling.
 8. A mechanical fuse (20) according to claim 4 wherein the second portion is glued or laser welded to the housing (60).
 9. A mechanical fuse (20) according to claim 1 wherein the housing (60) is arranged to encompass the rupture element (50).
 10. A mechanical fuse (20) according to claim 9 wherein the housing (60) and the rupture element (50) have a mating cylindrical shape.
 11. A mechanical fuse according claim 10 wherein the mating shape is arranged to prevent a rotation of the first coupling means (40) relative to the second coupling means (45).
 12. A mechanical fuse (20) according to claim 1 wherein the predetermined fuse force is in the range of 30 to 100 N.
 13. A mechanical fuse (20) according to claim 12 wherein the predetermined fuse force is in the range of 40 to 50 N.
 14. A mechanical fuse (20) according to claim 1 wherein the rupture element (50) is made of POM or PBT.
 15. A neck cord (30) comprising a mechanical fuse (20) according to claim
 1. 16. A method of connecting a mechanical fuse (20) according to claim 10 to a neck cord (30) having two end portions, the method comprising the steps of: putting one of the neck cord end portions through the open ends of the housing (60), coupling of the neck cord end portions to the first and second coupling means (40, 45), moving the housing over the rupture element (50) such that the housing engages with the rupture element at either side of the break plane.
 17. A method of connecting a mechanical fuse (20) according to claim 16 further comprising the step of glueing or welding the second portion of the rupture element (50) to the housing (60). 